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UBC Theses and Dissertations

Effects of stress path and prestrain history on the undrained monotonic and cyclic loading behaviour of saturated sand Chung, Edwin Kwok Fai


Stress path and prestrain effects on the monotonic and cyclic undrained behaviour of a saturated sand are investigated in the triaxial test. It is shown that under Identical consolidation stresses, the sand is contractive over a much larger range of relative densities in triaxial extension than in triaxial compression. The effective stress ratio at the initiation of contractive deformation (CSR) in extension is less than that in compression. During cyclic loading this feature makes the extension phase of the loading more damaging than the compression phase. The unique relationship between void ratio and undrained strength at PT state (which is similar to steady state line) noted in compression does not hold in extension. A separate relationship seems to emerge in extension for each initial void ratio and all such relationships lie to the left of the compression relationship, implying smaller PT state strengths in extension than in compression at equal void ratios. A small prestrain history (stress state staying within CSR lines during prestraining) is shown not to alter the initially liquefiable character of sand. With no strain reversal on reloading, increasing prestrain strain level between CSR and PT lines makes the sand. Strain reversal on reloading, on the other hand, causes the sand to become more contractive with increasing prestrain history and may transform an initially dilative to contractive sand.

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